I. Field of the Invention
The present invention relates to a throttle position sensor for an electronic throttle.
II. Description of Related Art
There are many previously known electronic throttles, also known as throttle by wire, of the type used in automotive engines. These previously known electronic throttles typically include a DC servo drive which moves a throttle element to control the airflow into the intake manifold of the engine. Such electronic throttles enjoy a number of advantages.
For example, with an electronic throttle control, the engine electronic control unit, typically a microprocessor, can be programmed to include traction control, cruise control and turbo anti-lag without additional hardware costs. Furthermore, since the actual throttle opening is controlled by the electronic control unit for the engine, by simple programming, the electronic control unit can be programmed to control the position of the throttle to minimize engine emissions, maximize engine economy, as well as controlling other aspects of the vehicle engine operation.
Such electronic throttles typically include a throttle position sensor which provides a feedback signal to the electronic control unit for the engine indicative of the precise position of the movable throttle element which controls the airflow to the intake manifold, typically a throttle plate. These previously known throttle position sensors typically comprise an elongated resistive strip having a first end and a second end. The strip may be either linear or, more commonly, arranged in a circular pattern.
A first voltage potential is electrically connected to the first end of the resistive strip while a second and different voltage potential, typically ground, is electrically connected to the second end of the resistive strip. An elongated wiper is then mechanically connected to the movable throttle element, i.e. the throttle plate, so that the point of contact between the wiper and the resistive strip varies as a function at the degree of opening of the throttle plate. Consequently, the voltage potential of the wiper varies proportionally with the position of the wiper relative to the resistive strip.
Ideally, the voltage output signal from the wiper varies linearly as the wiper moves from the first and towards the second end of the resistive strip. However, in practice, the previously known throttle position sensors do not exhibit such linearity, particularly after extended use of the throttle position sensor.
For example, in some cases the resistive strip becomes pitted or otherwise damaged on its surface. When this occurs, the desired constant contact between the wiper and the resistive strip is not maintained when the wiper moves across the damaged portion of the resistive strip. Instead, the contact resistance between the wiper and the resistive strip typically increases dramatically and results in a false voltage output reading on the wiper and thus from the sensor. Such a false output reading is then interpreted by the electronic control unit as an incorrect throttle opening position.
A still further problem with throttle position sensors is that the resistance of the resistive strip may change after extended use. When this occurs, improper engine operation can result.
Similarly, in some cases the wiper may become damaged or its attachment to the throttle position sensor damaged or loosened. When this occurs, in a manner similar to a damaged resistive strip, the contact resistance between the wiper and the resistive strip can vary widely thus providing a false output signal from the sensor as to the actual position of the throttle plate.
An incorrect output signal from the throttle position sensor due to a sudden increase of the contact resistance between the wiper and the resistive strip in many cases adversely affects the overall operation of the engine. For example, such inaccurate output signals from the throttle position sensor can result in hunting by the electronic throttle which eventually can cause some malfunction error codes. This adversely affects proper engine performance and, in some cases, can even adversely affect engine emissions and economy.
There have been no previously known throttle position sensors with circuitry capable of monitoring the contact resistance between the wiper and the resistive strip and/or compensating for incorrect outputs from the throttle position sensor.